Preheat the oven to 180°C (160°C fan) mark 4. Grease and line a 20.5cm (8in) square tin with baking parchment.

Put the butter and 150g (5oz) chocolate in a heat-proof bowl set over a pan of barely simmering water and stir frequently, until melted and smooth (alternatively, microwave in 30sec bursts). Take off the heat.

In turn, beat in the sugar, then the eggs and then the vanilla with a wooden spoon. Sift over the flour and cocoa powder and stir to make a smooth batter.

Pour the mixture into the prepared tin and spread to the edges. Bake for 20-25min or until there is no wobble left when you gently shake the tin.

Preheat the grill to high. Sprinkle the marshmallows over the brownie. Poke the broken biscuits into the top and dot over the remaining chocolate pieces. Grill for 30sec-1min, or until the marshmallow is lightly golden (don’t over cook in order to melt the marshmallows, as they will burn – if they aren’t melting down, remove from grill and gently squish them with the back of a spoon and grill for another 30sec. They will continue to melt and form a layer in the residual heat as the brownie cools).

Allow to cool completely in the tin before slicing (see GH Tip) or alternatively, cool for 15min and serve warm.

GH Tip

To get neater slices from your brownies, chill the brownies for at least 3hr or overnight to firm up. Allow to come up to room temperature before removing from the tin, then wet a knife under a running tap to stop the marshmallow from sticking to the blade, shake off the excess water and cut brownie into squares, wiping and wetting the knife for each cut.

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